Use this for questions relating to the proper use of physics terminology or nomenclature.
15
votes
2answers
119 views
What is a “Trojan Moon”?
Today I read an article about Saturn's moon Helene, and it was described as a "Trojan Moon" but no further explanation was given. It was difficult to even get any context about the term from the ...
15
votes
1answer
1k views
Differentiating Propagator, Greens function, Correlation function, etc
For the following quantities respectively, could someone write down the common definitions, their meaning, the field of study in which one would typically find these under their actual name, and most ...
14
votes
4answers
2k views
Are matrices and second rank tensors the same thing?
Tensors are mathematical objects that are needed in physics to define certain quantities. I have a couple of questions regarding them that need to be clarified:
1-Are matrices and second rank tensors ...
14
votes
2answers
700 views
Definitions: 'locality' vs 'causality'
I'm having trouble unambiguously interpreting many answers here due to the fact that the terms locality and causality are sometimes used interchangeably, while other times seem to mean very different ...
13
votes
7answers
1k views
What is a general definition of impedance?
Impedance is a concept that shows up in any area of physics concerning waves. In transmission lines, impedance is the ratio of voltage to current. In optics, index of refraction plays a role similar ...
11
votes
4answers
1k views
Does Earth have a code name?
Everything we discover in the sky get eventually a code name, like NGC 7293, Simeis 147, etc.
Does Earth/Moon have a code name too? Or it is just Earth/Moon, etc.?
11
votes
3answers
484 views
“Slightly off-shell”?
I'm not new to QFT, yet there are some matters which are quite puzzling to me. I often come across the statement that real particles (the ones we actually measure in experiments, not virtual ones) are ...
10
votes
2answers
3k views
What's the difference between inclusive and exclusive decays?
For example, why is the semileptonic $B$ decay $B \to X\ell\nu$ inclusive?
I can't find any definition of these frequently used terms, strange.
10
votes
3answers
236 views
The notion of an adiabatic process in thermodynamics -vs- quantum mechanics
I'm confused about the terminology in the two contexts since I can't figure out if they have a similar motivation. Afaik, the definitions state that quantum processes should be very slow to be called ...
10
votes
8answers
3k views
+50
What is the difference between electric potential, voltage and electromotive force?
This is a confused part ever since I started learning electricity. What is the difference between voltage and electromotive force (emf)? Both of them have the same SI unit, right? I would appreciate ...
10
votes
1answer
671 views
What came first, Rice Crispy or “Snap,” “Crackle,” and “Pop”? [closed]
The fourth, fifth, and sixth derivatives of position are called "Snap" "Crackle" and "Pop". What came first, the rice crispy characters, or the physics units?
9
votes
3answers
2k views
What's the difference between an entangled state, a superposed state and a cat state?
1) Can a state be entangled without also being a superposition? (Please give an example.)
2) Can a state be a superposition without being entangled? (Again, an example please.)
3) And what about ...
9
votes
4answers
266 views
Is the Lagrangian of a quantum field really a 'functional'?
Weinberg says, page 299, The quantum theory of fields, Vol 1, that
The Lagrangian is, in general, a functional $L[\Psi(t),\dot{\Psi}(t)$], of a set of generic fields $\Psi[x,t]$ and their time ...
9
votes
2answers
231 views
Word for the star around which an exoplanet orbits:
Is there accepted nomenclature for the star around which a particular exoplanet orbits? Meaning, if I were to say "The exoplanet blah blah blah's (noun)" what noun would I put there? Sun? Star? ...
8
votes
8answers
979 views
What is the name of the principle saying it is meaningless to talk/ask questions that can not be measured/tested?
Watching quantum mechanics lectures and it was mentioned that it is pointless/meaningless to try to talk/question things that can not be tested/measured.
Is this a principle? And if so what is it's ...
8
votes
4answers
233 views
What makes an equation an 'equation of motion'?
Every now and then, I find myself reading papers/text talking about how this equation is a constraint but that equation is an equation of motion which satisfies this constraint.
For example, in the ...
7
votes
3answers
618 views
What does the dual of a tensor mean (e.g. dual stress tensor in relativistic ED)?
I know what the dual of a vector means (as a map to its field), and I am also
aware of of the definition a dual of a tensor as,
$$F^{*ij} = \frac{1}{2} \epsilon^{ijkl} F_{kl}\tag{1}$$
I just don't ...
7
votes
3answers
6k views
What exactly is the difference between radiation and convection?
Okay, so everywhere I've read, I hear the main difference is the requirement of a medium. But for example, if you take the case of heat 'radiating' from a red-hot iron, isn't that actually convection ...
7
votes
2answers
251 views
Should it be obvious that independent quantum states are composed by taking the tensor product?
My text introduces multi-quibt quantum states with the example of a state that can be "factored" into two (non-entangled) substates. It then goes on to suggest that it should be obvious1 that the ...
7
votes
1answer
231 views
What's the relation between perturbative and nonperturbative QFT?
In case of any miscommunication let me describe my understanding of the meaning of "perturbative" and "non-perturbative", and correct me if something is wrong:
In a perturbatively defined QFT the ...
6
votes
3answers
2k views
Why is Higgs Boson given the name “The God Particle”?
Higgs Boson (messenger particle of Higgs field) accounts for inertial mass, not gravitational mass.
So, how could it account for formation of universe as we know it today? I think, gravity accounts ...
6
votes
3answers
69 views
Do days and months on the Moon have names?
On Earth we have various calendars, for example,
Days: Monday, Tuesday, Wednesday, etc., etc.
Months: January, February, March
Does the Moon have names for its "daily" rotations, etc.?
It sounds ...
6
votes
1answer
1k views
Eigenfunctions v.s. eigenstates
Is there a difference between "eigenfunction" and "eigenstate"? They seem to be used interchangeably in texts, which is confusing. My guess is that an "eigenfunction" has an explicit ...
6
votes
1answer
327 views
Is Pauli-repulsion a “force” that is completely separate from the 4 fundamental forces?
You can have two electrons that experience each other's force by the exchange of photons (i.e. the electromagnetic force). Yet if you compress them really strongly, the electromagnetic interaction ...
5
votes
5answers
564 views
Difference between theoretical physics and mathematical physics?
I'm a huge fan of mathematical physics and I know what the formal definitions of those two areas are, I've seen them. But I still get completely baffled when someone asks me to explain it simply. The ...
5
votes
3answers
3k views
What is the official difference between a planet and a dwarf planet?
I'm trying to understand how objects are classified as planets, moons, or dwarf planets. Can someone please explain the differences between them? I'm really curious about why Pluto is a dwarf planet, ...
5
votes
2answers
189 views
Nomenclature of hadronic resonances
I have the Particles Physics Booklet and I noticed that the resonances that decay into a nucleon and pion are indicated by an abbreviation. For example $P_{33}$ is associated to the $\Delta (1232)$ ...
5
votes
3answers
180 views
What is a “measure equation” as mentioned by this TeX Users Group guide?
In this TeX Users Group (TUG) document, Typesetting mathematics for science and technology according to ISO 31/XI by Claudio Beccari, the author makes various typesetting recommendations including:
...
5
votes
1answer
200 views
Nomenclature of radial solutions to the Schrodinger Equation
For the free particle with quantum number $l=0$, the regular solution to the radial Schrodinger equation is $R_0 (\rho)=\frac{\sin{\rho}}{\rho}$ while the irregular solution is $R_0 ...
5
votes
1answer
59 views
Is there an established standard for naming exoplanets?
I understand that exoplanets are named by adding a lowercase letter to the a designation of the planet's parent star or stellar system, beginning with 'b' (the star itself is 'a') in order of ...
5
votes
2answers
504 views
What is “code” in “toric code”?
When I first heard people talking about using Kitaev's toric code to do topological quantum computation, I was thinking how many lines does the toric code have. Then I was told that
the "code" really ...
5
votes
2answers
228 views
What's the difference between “evidence of a new particle” and “discovery of a new particle”?
Today’s exciting press release from Tevatron on the Higgs boson keeps its head cool and say that physicists saw a “hint” of the Higgs boson because the signal is barely above the two-sigma level. In ...
5
votes
1answer
380 views
What does the concept of phase space mean in particle physics?
I came across the concept of phase space in statistical mechanics.
How does this concept come about in particle physics?
Why was it introduced and how is it used?
What does it mean when ...
5
votes
2answers
94 views
Is the “dimension” in dimensional analysis the same as the “dimension” in “three spatial dimensions”?
When we talk about the dimension of a quantity (e.g. the dimension of acceleration is$[ L \ T ^ {-2}]$) are we talking about the same "dimension" as when we talk about three dimensional space?
Are ...
5
votes
2answers
107 views
What is it called when a fluid will “jump” to grab onto an object that comes very close?
I'm doing an experiment where I bring a probe very close to a well full of fluid and then very slowly lower it to obtain some force deformation values. The material behaves very much like a fluid and ...
5
votes
0answers
163 views
Physical interpretation: weighted eigenvalues of the Laplacian with a potential
I'm a mathematician with only the basic knowledge of Physics, so my question may be trivial: in this case, mercy me. :-)
Let $\Omega \subseteq \mathbb{R}^N$ be a domain and let $V,m:\Omega \to ...
4
votes
4answers
5k views
What's the difference between Fermi Energy and Fermi Level?
I'm a bit confused about the difference between these two concepts. According to Wikipedia the Fermi energy and Fermi level are closely related concepts. From my understanding, the Fermi energy is the ...
4
votes
2answers
230 views
What does a non-perturbative theory mean?
I'm a science writer and I'm having difficulty understanding what a non-perturbative approach means. I thought I understood what perturbative meant, but in looking for explanations of ...
4
votes
3answers
478 views
Nomenclature: Yang-Mills theory vs Gauge theory
If you're writing about a theory with Yang-Mills/Gauge fields for an arbitrary reductive gauge group coupled to arbitrary matter fields in some representation,
is it best to call it a Yang-Mills ...
4
votes
2answers
338 views
Amplitude of Probability amplitude. Which one is it?
QM begins with a Born's rule which states that probability $P$ is equal to a modulus square of probability amplitude $\psi$:
$$P = \left|\psi\right|^2.$$
If I write down a wave function like this ...
4
votes
3answers
304 views
Are quantum mechanics and quantum physics the same field?
What is the difference between quantum mechanics and quantum physics?
4
votes
4answers
171 views
What is the term for hose fluctuating movements during flow?
What do we call it when water flowing through a flexible hose causes it to act like snake movements if the hose were disturbed?
Can this movement be explained by the Coriolis force?
4
votes
1answer
145 views
What is the difference between Radiation and Electromagnetic Radiation
Are the two equivalent or is Electromagnetic Radiation a subset of Radiation. I am further confused by the fact that electromagnetic radiation includes both ionizing and non ionizing types of ...
4
votes
1answer
368 views
Is there a difference between a postulate and a principle in physics?
Is there a difference between a postulate and a principle in physics?
Both seem unproved statements taken as true. If thats correct, why the different names?
4
votes
1answer
4k views
What exactly is the difference between advection and convection?
After reading Wikipedia articles on advection and convection, I still cannot determine whether there is a consensus on a difference between these two terms.
Sometimes, the term convection seems to ...
4
votes
2answers
2k views
Convective and Diffusive terms in Navier Stokes Equations
My question has 2 parts:
I just followed the derivation of Navier Stokes (for Control Volume CFD analysis) and was able to understand most parts. However, the book I use (by Versteeg) does not ...
4
votes
1answer
588 views
Mnemonics for remembering physical data
Anyone have good mnemonics for remembering standard packets of data in physics?
Any field within physics would be welcomed. Examples of such "packets":
data in the standard model of particle ...
4
votes
2answers
435 views
The definition of “frequency” in different contexts
I have been doing some research on all kinds of sound-related topics lately and have been a bit confused by the different uses of the term "frequency". Of course, the most general meaning of frequency ...
3
votes
2answers
305 views
What is a single word that describes the idea of the second time derivative of energy?
I think about position, its time derivative speed, and its second time derivative, acceleration. I would like to identify a single word that can be used as a handle for the second time derivative of ...
3
votes
3answers
187 views
What is “A” in AGeV?
AGeV means GeV per nucleon. But why A letter is used for such a short cut? Why not NGeV, for example?
